.TH LTTNG_HEALTH_CHECK 3 2012-09-19 "LTTng" "LTTng Developer Manual"
.SH NAME
.B DEPRECATED

lttng_health_check \- Monitor health of the session daemon
.SH SYNOPSIS
.nf
.B #include <lttng/lttng.h>
.sp
.BI "int lttng_health_check(enum lttng_health_component c);
.fi

Link with -llttng-ctl.
.SH DESCRIPTION
The
.BR lttng_health_check ()
is used to check the session daemon health for either a specific component
.BR c
or for all of them. Each component represent a subsystem of the session daemon.
Those components are set with health counters that are atomically incremented
once reached. An even value indicates progress in the execution of the
component. An odd value means that the code has entered a blocking state which
is not a poll(7) wait period.

A bad health is defined by a fatal error code path reached or any IPC used in
the session daemon that was blocked for more than 20 seconds (default timeout).
The condition for this bad health to be detected is that one or many of the
counters are odd.

The health check mechanism of the session daemon can only be reached through
the health socket which is a different one from the command and the application
socket. An isolated thread serves this socket and only computes the health
counters across the code when asked by the lttng control library (using this
call). This subsystem is highly unlikely to fail due to its simplicity.

The
.BR c
argument can be one of the following values:
.TP
.BR LTTNG_HEALTH_CMD
Command subsystem which handles user commands coming from the liblttng-ctl or
the
.BR lttng(1)
command line interface.
.TP
.BR LTTNG_HEALTH_APP_MANAGE
The session daemon manages application socket in order to route client command
and check if they get closed which indicates the application shutdown.
.TP
.BR LTTNG_HEALTH_APP_REG
The application registration mechanism is an important and vital part of for
user space tracing. Upon startup, applications instrumented with
.BR lttng-ust(3)
try to register to the session daemon through this subsystem.
.TP
.BR LTTNG_HEALTH_KERNEL
Monitor the Kernel tracer streams and main channel of communication
(/proc/lttng). If this component malfunction, the Kernel tracer is not usable
anymore by lttng-tools.
.TP
.BR LTTNG_HEALTH_CONSUMER
The session daemon can spawn up to
.BR three
consumer daemon for kernel, user space 32 and 64 bit. This subsystem monitors
the consumer daemon(s). A bad health state means that the consumer(s) are not
usable anymore hence likely making tracing not usable.
.TP
.BR LTTNG_HEALTH_ALL
Check all components. If only one of them is in a bad state, a health check
error is returned.

.SH "RETURN VALUE"
Return 0 if the health is OK, or 1 is it's in a bad state. A return code of \-1
indicates that the control library was not able to connect to the session
daemon health socket.

.SH "LIMITATIONS"

For the LTTNG_HEALTH_CONSUMER, you can not know which consumer daemon has
failed but only that either the consumer subsystem has failed or that a
lttng-consumerd died.

.SH "AUTHORS"
lttng-health-check was originally written by David Goulet and is currently
maintained by Jérémie Galarneau <jeremie.galarneau@efficios.com>.
